1. Field of the Invention
This invention relates to a packaging material for photosensitive materials for photographic purpose.
2. Description of Prior Arts
Various types of packaging materials for photosensitive materials for photographic purpose (hereafter simply referred to as "photosensitive materials") have been put to practical use, and various properties are required according to their uses.
As a packaging material for photosensitive materials, it is necessary to have various properties such as light-shielding, gas barrier, moisture proofing, physical strength such as breaking strength, tear strength, impact puncture strength, Gelbo test strength and wear resistance, heat sealing properties such as heat seal strength, hot tack properties (hot-seal ability), and seal ability of contraries antistatic properties, flatness, slipping character and the like. Generally, it is difficult to satisfy these properties by a single material, and a single layer film of a high-pressure low-density polyethylene (LDPE) kneaded with carbon black or a pigment as shown in FIG. 21 or a laminated film composed of LDPE and a flexible sheet such as paper, aluminum foil or cellophane, etc. has been employed. An example of the conventional laminated film is shown in FIG. 22. This film is composed of a light-shielding LDPE film layer 7a, a light-shielding metal foil layer 4a laminated to it through an adhesive layer 2, and a flexible sheet layer 3 laminated thereupon through an adhesive layer 2.
On the other hand, the present inventor has already disclosed a laminated film for packaging photosensitive materials having improved physical strength by combining two uniaxially stretched films (U.S. Pat. No. 4,331,725). With respect to the packaging material containing a low-pressure linear low-density polyethylene (L-LDPE), a packaging material comprising at least one light-shielding film layer of polyethylene polymer of which more than 50 wt.% is L-LDPE and containing more than 1 wt.% of a light-shielding material has been disclosed (U.S. Pat. No. 4,452,846). A packaging material has been developed comprising a metallized film layer and two polyethylene polymer layers both of which contain more than 50 wt.% of L-LDPE, at least one of which layers contains a light-shielding material and which are laminated on both sides of the metallized film layer (U.S. Ser. No. 769,573). Both polyethylene polymer layers have particular relationships in strength and in the difference in thickness of the layers.
Physical properties of the conventional laminated films are not satisfactory, and during packaging, the films are sometimes torn or punctured or the heat of the films sometimes separated. In addition, when a large amount of a light-shielding material such as carbon black is added, physical strength of the film is lowered. When, the amount was set at about 3%, thickness of the film was more than 70 .mu.m. As the result, the film was stiff, and working efficiency of the packaging process was adversely affected. Cost of the packaging was also expensive.
In the case of the laminated film disclosed in the specification of U.S. Pat. No. 4,331,725, since two layers of uniaxially stretched film are necessary, the laminated film is thick and expensive as a packaging material, though physical properties such as tear strength are improved.
The packaging material disclosed in the specification of U.S. Pat. No. 4,452,846 has also various problems in the formation of film, in the occurrence of blocking between films, in bad affect upon photosensitive materials such as fogging and increase or decrease of photosensitivity, in insufficient slipping character between films, in insufficient slipping character against photosensitive materials, in the occurrence of blocking against photosensitive materials, and in insufficient packaging character against photosensitive materials.